This invention relates to a mechanical knee joint and method. More particularly, the invention relates to a knee orthosis or knee-ankle-foot orthosis and a mechanical knee joint incorporating a spring to control knee flexion and a method of providing desired resistance during knee flexion by use of the joint.
Orthotic knee devices traditionally are utilized to aid and support guiding and limiting the range of motion of the human knee joint. A mechanical knee joint is frequently used to pivotally connect portions of the orthotic device secured to the body above and below the knee joint. Such a mechanical joint permits relative movement of the members and the associated body limbs and joints, to which the members are attached and the body joint to which the body parts are connected.
Typically a normal, healthy person flexes his or her knee through a range of about 18xc2x0 from full extension during the loading response aspect of a normal gait cycle. During the normal stride of a normal person, there is a certain amount of natural muscle resistance during knee flexion in the quadriceps and hip muscles, for example. A patient with weak quadriceps muscles caused by, for example, polio, may have difficulty walking because the patient""s knee can buckle during walking. A need exists for a knee joint that simulates the resistance that an individual encounters during a normal walking stride. A need also exists for a knee joint that can provide different amounts of resistance depending upon the muscle strength of a particular patient. A need exists for a knee joint that is easily adjustable among several different degrees of resistance. A need also exists for a knee joint and knee orthosis that provides a relatively constant resistance throughout the flexion movement and can be preloaded to a set amount of resistance when the joint is in the full extension position. A further need exists for a knee joint that provides such resistance without requiring numerous precise parts that require close tolerances.
In accordance with the present invention, a mechanical knee joint connecting two members for limited relative pivotal motion or movement is provided that provides resistant knee flexion. The orthotic knee joint comprises two members that are typically elongated, a structure associated with each member for permitting pivotal movement of one member relative to the other between extension and flexion positions and a torsion spring operatively associated with the bar members to provide torsional resistance to restrain pivotal movement of the bar members between the extension and flexion positions.
In accordance with another aspect of the present invention, a mechanical orthotic knee joint for pivotally connecting two orthotic members around an axis of rotation is provided comprising an upper and lower member, a structure associated with and connecting the upper and lower members for permitting movement of those members between extension and flexion positions and a torsion spring that is operatively associated with the members and extends longitudinally along the joint and one of the members to provide resistance to restrain pivotal movement.
Another aspect of the invention provides an orthotic appliance comprising a foot support, a lower bar member, an upper bar member, an orthotic ankle joint for pivotally connecting the foot support to the lower bar member, a first knee joint for permitting pivotal movement of the lower bar member relative to the upper bar member, a second knee joint for locking and releasing the upper bar member relative to the lower bar member such as when the wearer is in a sitting position, and a torsion spring to provide resistance during movement of the bar members from an extension position to a flexion position during rotational movement of the first knee joint.
Yet another aspect of the present invention is a method of providing a desired amount of resistance during flexion of a mechanical orthotic knee joint that comprises the steps of inserting a torsion spring into an orthotic device comprising two bar members connected by a mechanical knee joint.
Yet a further aspect of the present invention is a method of providing a uniform degree of resistance for a person wearing a knee joint comprising providing a knee joint of the present invention, wearing the device in any operative position on at least one of a patient""s knees and walking with the knee joint in the operative position so that a desired level of resistance is achieved.
In one embodiment of the present invention, a torsion spring is loaded during flexion of the bar members. The loading of the torsion spring in the full extension position, as well as the type and size of the spring, determine the resistance in the joint. The torsion spring may also be used to limit the pivotal movement of the device.
In accordance with another aspect of the invention, the desired resistance in knee flexion can be easily and quickly adjusted to provide a greater or lesser amount of resistance. Torsion springs with different characteristics such as having different dimensions or composed of different materials may be readily removed from or inserted into the joint. In one embodiment of the present invention, the preload of tension in the torsion spring in the device can be adjusted. The amount of preload helps determine the initial resistance of the torsion spring in the fully extended position and aids in simulating the resistance and support during the walking stride of a healthy individual.
In accordance with yet another aspect of the present invention, the resistance during flexion is relatively constant. In the preferred embodiment, a substantial resistance can be obtained readily by use of a spiral torsion spring. In addition, the device of the present invention may be constructed to allow for different maximum ranges of flexion for different walking strides.
In accordance with another aspect of the present invention, one end of the torsion spring is operatively attached directly or indirectly to the upper member. Another end of the torsion spring is operatively attached to the lower member. To cause the lower member to pivot about the joint, sufficient force must be supplied to overcome the resistance of the torsion spring to compression.
Another aspect of the present invention provides a mechanical knee joint that is relatively simple to assemble, reliable and economical. The present invention uses a small number of parts and these parts to provide the desired resistance do not need to be machined or fabricated to close tolerances to work effectively.
For purposes of the present invention, xe2x80x9ctorsion springxe2x80x9d means a spiral torsion spring or leaf spring, including but not limited to a rectangular plate spring, triangular plate spring, rectangular plate spring with end tapered, compound leaf and laminated springs, laminated triangular plate springs, laminated rectangular plate spring with leaf ends tapered, laminated trapezoidal plate springs with leaf ends tapered, semielliptic springs, elliptic springs and spiral coil torsion springs of rectangular cross section. The preferred embodiment of the present invention utilizes a spiral torsion spring.